KR20150113770A - Negative electrode active material for nonaqueous electrolyte rechargeable battery and rechargeable battery including the same - Google Patents

Abstract

The present invention relates to an anode material for a nonaqueous electrolyte secondary battery, a method for producing the same, and a nonaqueous electrolyte secondary battery comprising the same. More particularly, the present invention relates to an anode material for a nonaqueous electrolyte secondary battery using a carbonaceous nanofiber and a carbon- And a nonaqueous electrolyte secondary battery comprising the same.
The negative electrode material for a non-aqueous electrolyte secondary battery according to the present invention can suppress the volume change of the negative electrode active material, improve the adhesion between the negative electrode active material in the negative electrode and the electric conductivity, maintain the high battery capacity of the negative electrode silicon oxide, , And exhibits an excellent cycle property.

Description

TECHNICAL FIELD The present invention relates to an anode material for a nonaqueous electrolyte secondary battery, a method for manufacturing the same, and a nonaqueous electrolyte secondary battery including the same. [0002]

The present invention relates to an anode material for a nonaqueous electrolyte secondary battery, a method for producing the same, and a nonaqueous electrolyte secondary battery comprising the same. More particularly, the present invention relates to an anode material for a nonaqueous electrolyte secondary battery using a carbonaceous nanofiber and a carbon- And a nonaqueous electrolyte secondary battery comprising the same.

2. Description of the Related Art In recent years, development of a secondary battery having a high energy density has been strongly demanded from the viewpoints of economical efficiency, miniaturization of a device, and reduction in weight, along with remarkable development of portable electronic devices and communication devices. At present, secondary batteries of high energy density include nickel cadmium batteries, nickel hydrogen batteries, lithium ion secondary batteries and polymer batteries. Of these, the lithium ion secondary battery is remarkably long-life and high-capacity compared to the nickel-cadmium battery and the nickel-metal hydride battery.

Conventionally, as a negative electrode active material of a lithium ion secondary battery, a carbon-based material has been used. A composite oxide of lithium and boron, a complex oxide of lithium and a transition metal (V, Fe, Cr, Mo, Ni and the like), a composite oxide of Si, Ge or Sn and a lithium- N and O, and Si particles whose surface is covered with a carbon layer by chemical vapor deposition.

However, all of these negative electrode active materials can improve the charge / discharge capacity and increase the energy density, but the expansion and shrinkage of lithium ion storage and release are increased. Therefore, the lithium ion secondary battery using these negative electrode active materials has insufficient retention of discharge capacity (hereinafter referred to as " cycle characteristics ") due to repetition of charging and discharging.

On the other hand, it has been attempted to use, as the negative electrode active material, a powder of silicon oxide represented by SiOx (0 < x? 2) such as SiO 2.

The silicon oxide can be expressed as SiOx (where x is a mole ratio of O / Si, which is slightly larger than 1 of the theoretical value). However, analysis by transmission electron microscopy shows that the crystalline silicon from amorphous to several tens of nm is finely dispersed in the silicon oxide Lt; / RTI &gt; Therefore, the battery capacity is smaller than that of silicon but is 5 to 6 times higher than that of carbon, and the volume expansion is also small, and it is thought that it is easy to use as a negative electrode active material. However, since silicon oxide has a large irreversible capacity and a very low initial efficiency of about 70%, it is necessary to increase the capacity of the anode in excess of the capacity of the anode in the case of actually fabricating the battery, There is a problem that an increase in capacity can not be expected.

In Patent Document 1, it has been described that the effect of the composite of SiOx and amorphous aluminum oxide (Al ₂ O ₃ ), which is an anode material, suppresses the volume expansion of silicon to improve secondary battery life characteristics. However, There is room for improvement in improving lifetime characteristics.

In Patent Document 2, when the surface of the silicon oxide particles is coated with a metal oxide and used in a secondary battery, the amount of gas generated due to the decomposition of the electrolytic solution can be reduced without substantially reducing the charge capacity and the discharge capacity, .

In Patent Document 3, only silicon particles coated with carbon nanotubes, carbon nanofibers or carbon fibers among the composite particles of silicon oxide and Si particles are limited.

[Patent Document 1] JP-A-2010-55775 [Patent Document 2] Japanese Patent Application Laid-Open No. 11-96455 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-99341

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a SiO.sub.2 composite containing silicon, silicon oxide, aluminum oxide, carbon nanofibers, and carbon, and a method of manufacturing the same.

The present invention also provides a negative electrode and a nonaqueous electrolyte secondary battery for a nonaqueous electrolyte secondary battery using the aluminum oxide silicon composite according to the present invention.

The present invention provides an anode material for a non-aqueous electrolyte secondary battery, which is a SiO 2 composite containing silicon, silicon oxide, aluminum oxide, carbon nanofibers, and carbon to solve the above problems.

The negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention has an Si content of 30 to 60 mass%, an oxygen content of 20 to 40 mass%, an Al content of 0.1 to 20 mass%, a carbon nanofiber and a carbon content of 1 to 20 mass% .

The negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention has an average particle diameter of 0.1 to 30 탆 and a BET specific surface area of 0.5 to 50 m ² / g.

In the negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention, the average diameter of the carbon nanofibers is 10 nm to 100 nm and the length is 0.1 to 10 μm.

The present invention also relates to

A first step of preparing a compound represented by SiOx in which fine particles of silicon oxide and silicon are dispersed in a silicon-based compound;

A second step of mixing the compound represented by SiOx with aluminum powder;

A third step of heat-treating the mixture at 600 to 1100 占 폚; And

A fourth step of coating the surface with carbon nanofibers and carbon by CVD at 600 to 1100 占 폚; The present invention also provides a method of manufacturing an anode material for a nonaqueous electrolyte secondary battery according to the present invention.

In the method for producing an anode material for a nonaqueous electrolyte secondary cell according to the present invention, the SiOAl composite can be obtained by reacting silicon oxide with aluminum. Here, the silicon oxide is usually produced by heating a mixture of silicon dioxide (SiO ₂ ) and silicon under a reduced pressure condition at a temperature in the range of 1,300 to 1,500 ° C to produce a silicon oxide gas and cooling the silicon oxide gas at about 500 to 900 ° C to obtain amorphous silicon Oxide. The silicon oxide is represented by the general formula SiOx. The range of x of the precipitate is preferably 0.9 <x <1.5 and more preferably 1.0 x 1.1 by N / O analysis (Nitrogen / Oxygen analysis). The molar ratio of silicon dioxide to silicon is generally 1: 1.

In the method for manufacturing an anode material for a nonaqueous electrolyte secondary cell according to the present invention, the silicon oxide generates silicon and aluminum oxide by a reductive reaction with aluminum according to the following reaction formula.

3 SiO + 2 Al - &gt; 3Si + Al ₂ O ₃

In the method for manufacturing an anode material for a nonaqueous electrolyte secondary battery according to the present invention, the average particle diameter of the silicon oxide in the second step is 0.1 to 30 탆, and the particle diameter of the aluminum powder is 1 to 20 탆.

In the method for producing an anode material for a nonaqueous electrolyte secondary battery according to the present invention, when the particle size of silicon oxide is smaller than the above range, the specific surface area becomes large, so that uniform mixing is difficult during the production of the electrode slurry of the secondary battery and consumption of the amount of the binder is increased, There are difficulties in manufacturing.

In the method of manufacturing an anode material for a nonaqueous electrolyte secondary cell according to the present invention, when the aluminum powder is 1 μm or less, the oxygen content due to the rapid oxidation of the aluminum powder in the atmosphere during the mixing with silicon or silicon oxide can be rapidly increased, There may be difficulties in handling. If the aluminum powder is 20 mu m or more, the distribution of aluminum oxide, which is a product, may be uneven due to the reaction with silicon oxide, and the quality of the anode material may be deteriorated.

In addition, since there is a risk of ignition in the handling of the Al powder, liquid mixing is preferred rather than dry mixing in the case of mixing with silicon oxide.

In the method for manufacturing an anode material for a nonaqueous electrolyte secondary cell according to the present invention, it is preferable that the mixture is heat-treated at 600 to 1100 ° C. If the heat treatment temperature is 600 ° C or lower, the reaction between aluminum and silicon oxide is less likely to occur due to the lower melting point of aluminum, and unreacted aluminum particles may remain. If the temperature is higher than 1100 ° C, Alumina (Al ₂ O ₃ ) generation is performed well by the reaction of the silicon oxide, but the non-uniformity of the silicon oxide is intensified and the crystallinity of the particles of the phase-separated Si is increased, and the lifetime characteristics of the anode material may be deteriorated.

The heat treatment time is appropriately selected and varies depending on the shape of the reactor and the mass of the reactant, but is preferably 1 to 10 hours, more preferably 2 to 7 hours.

In the method for manufacturing an anode material for a non-aqueous electrolyte secondary cell according to the present invention, if the content of aluminum powder is 0.1% or less, the effect of addition of aluminum is not generated, and if the content of aluminum powder is 20% The effect of improving the negative electrode material may be deteriorated.

In the method for producing an anode material for a nonaqueous electrolyte secondary battery according to the present invention, a reaction product of silicon oxide and Al after heat treatment is subjected to a chemical vapor deposition (CVD) treatment or a mechanical It is preferable to obtain a SiO 2 composite that is surface-treated with carbon nanofibers and carbon by mixing, and more preferably, a SiO 2 composite is obtained by chemical vapor deposition. As described above, the carbon material surface-treated on the SiO 2 composite is a carbon nanofiber, Carbon nanotubes and the like may be included depending on the type of hydrocarbon, heat treatment temperature, chemical vapor deposition method and the like, not limited to carbon.

In the method for producing an anode material for a non-aqueous electrolyte secondary cell according to the present invention, it is preferable that the product of SiO and Al be treated with a hydrocarbon compound gas or vapor at 600 to 1,100 DEG C under normal pressure or reduced pressure , More preferably 700 to 1,000 占 폚, to form a carbon coating film containing carbon nanofibers on the surface of the particles. The disposition time is appropriately selected according to the target amount of carbon coating, the treatment temperature organic gas concentration (flow rate), the amount of introduction, and the like, but usually 1 to 10 hours, especially 2 to 7 hours, It is efficient.

The present invention also provides a negative electrode for a nonaqueous electrolyte secondary battery comprising the negative electrode material for a nonaqueous electrolyte secondary battery of the present invention and a nonaqueous electrolyte secondary battery comprising the same.

The negative electrode material for a nonaqueous electrolyte secondary battery according to the present invention suppresses the volume change of the negative electrode active material, improves the adhesion between the negative electrode active materials in the negative electrode and the electrical conductivity, maintains a high battery capacity of the silicon oxide negative electrode, , And exhibits an excellent cycle property.

FIG. 1 shows SEM (Scanning Electron Microscope) photographs of a SiOA composite anode active material prepared according to an embodiment of the present invention. FIG. 2 shows TEM (Transmission Electron Microscope, JEM2100F / JEOL).
FIG. 3 shows the results of XRD measurement of Sample 3 in which silicon oxide and aluminum powder were mixed at a mass ratio of 9: 1 and then heat-treated at 750 ° C for 3 hours, and FIG. 4 shows a result of mixing XRD and aluminum powder at a mass ratio of 9: XRD measurement results of a SiO 2 composite sample 3 obtained by heat-treating at 750 ° C for 3 hours and then subjecting the powder to CVD treatment under a mixed gas of argon (Ar) and methane (CH ₄ ) at 1000 ° C for 2 hours are shown.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

< Example  1> SiOAl Negative active material  making

(BET specific surface area 10.5 m ² / g) and an aluminum powder (average particle diameter D 50 = 3.6 μm) were mixed in a composition of silicon oxide / aluminum = 99.5 / 0.5, 95/5 and 90/10 After mixing and drying, Samples 1, 2 and 3 were prepared and heat treated in a tube furnace under the condition of argon (Ar) gas at 750 ° C for 3 hours, and then cooled to recover black brown powder. The recovered mixed powder showed almost no aggregation.

As a result of the ICP elemental analysis, the content of aluminum was 0.5, 5 and 10 mass%, respectively.

< Example  2> Carbon nano  Fiber coating SiOAl Negative active material  making

Samples 1 to 3 obtained after the heat treatment in Example 1 were placed in a tube furnace and subjected to a CVD treatment under a mixed gas of argon (Ar) and methane (CH ₄ ) at 1000 ° C for 2 hours to obtain carbon nanofibers and carbon- SiOA complex was obtained. Each of the samples 1 to 3 had a carbon content of 3% and 4%. 3.3% and the BET specific surface area was as follows.

division BET specific surface area Sample 1 19.6 m &lt; 2 &gt; / g Sample 2 24 m 2 / g Sample 3 22.4 m &lt; 2 &gt; / g

< Experimental Example > SEM  Photo measurement

SEM photographs and TEM photographs of the surface-coated carbon nanofibers of the sample 3 obtained in Example 2 were measured and shown in Figs. 1 and 2, respectively.

< Experimental Example > XRD  Measure

The sample 3 was heat-treated at 750 ° C for 3 hours to determine whether or not silicon oxide and aluminum were completely reacted with each other. The SiO 2 composite was chemically vapor-deposited at 1000 ° C for 2 hours. 4.

As shown in FIG. 3 and FIG. 4, after the heat treatment, the peak corresponding to aluminum was clearly observed, but after the chemical vapor deposition, the aluminum peak almost disappeared and the peak of aluminum oxide (Al ₂ O ₃ ) .

< Comparative Example > Anode active material  making

As a comparative example, oxide which does not contain an aluminum silicon powder (BET specific surface area of 1.6m ² / g) to 1000 ℃ by using a tube, CVD under an argon (Ar) and methane (CH ₄₎ gas mixture for 2 hours to To obtain a SiO powder having a 3% carbon content. The BET specific surface area was 2.7 m ² / g.

< Manufacturing example > Coin cell  making

The anode active material prepared in Example 2 and Comparative Example was mixed with Super-P black (Timcal) as a conductive material and PAA (Poly Acrylic acid, Aldrich) as a binder with a weight ratio of 80:10:10 to N-methyl Pyrrolidone to prepare a slurry-state composition.

This composition was applied to a copper foil having a thickness of 18 mu m and dried to form an active material layer having a thickness of 30 mu m on one side of the copper foil. Next, a test electrode was prepared by punching in a circle having a diameter of 14Φ. As the opposite electrode, a metal lithium foil having a thickness of 0.3 mm was used. As the separation membrane, a porous polyethylene sheet having a thickness of 0.1 mm was used. As the electrolytic solution, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1 at a concentration of about 1 mol / L as a lithium salt. These components were placed in a container made of stainless steel, and a coin cell for evaluation having a general shape of 2 mm in thickness and 32 mm in diameter (so-called 2032 type) was built.

< Manufacturing example > Evaluation of battery characteristics

The coin cell prepared for each sample was charged at a constant current of 0.05 C until the voltage became 0.01 V and discharged until the voltage became 1.5 V at a constant current of 0.05 C to obtain the discharge capacity and the initial efficiency. Was conducted at a constant current of 0.2 C in the same voltage range as above, and the capacity retention rate test was carried out. The results are shown in Table 2.

As shown in Table 2 below, it can be seen that the initial efficiency and the capacity retention rate of the sample 2 and the sample 3 negative electrode active material according to the embodiment of the present invention were improved by 30% or more as compared with the comparative example.

Initial efficiency (%)
(Discharge capacity / charge capacity) Discharge capacity
(mAh / g) Capacity retention rate (%)
(20 cycles) Sample 1 73 1460 76 Sample 2 76 1430 94 Sample 3 77 1370 88 Comparative Example 1 74 1450 60

Claims (8)

An anode material for a nonaqueous electrolyte secondary battery, which is a SiOAl composite containing silicon, silicon oxide, aluminum oxide, carbon nanofibers, and carbon.
The method according to claim 1,
Wherein the negative electrode material has an Si content of 30 to 60 mass%, an oxygen content of 20 to 40 mass%, an Al content of 0.1 to 20 mass%, a carbon nanofiber and a carbon content of 1 to 20 mass% Battery anode material
The method according to claim 1,
Wherein the negative electrode material has an average particle diameter of 0.1 to 30 占 퐉 and a BET specific surface area of 0.5 to 50 m ² / g. The nonaqueous electrolyte secondary battery anode material
The method according to claim 1,
Wherein the carbon nanofibers have an average diameter of 10 nm to 100 nm and a length of 0.1 to 10 μm. The nonaqueous electrolyte secondary battery anode material
A first step of preparing a compound represented by SiOx in which fine particles of silicon oxide and silicon are dispersed in a silicon-based compound;
A second step of mixing the compound represented by SiOx with aluminum powder;
A third step of heat-treating the mixture at 600 to 1100 占 폚; And
A fourth step of coating the surface with carbon nanofibers and carbon by CVD at 600 to 1100 占 폚; A method for manufacturing an anode material for a non-aqueous electrolyte secondary battery according to claim 1, comprising
6. The method of claim 5,
Wherein the aluminum powder in the second step has a particle diameter of 1 to 20 占 퐉.
A negative electrode for a nonaqueous electrolyte secondary battery comprising an anode material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4
A nonaqueous electrolyte secondary battery comprising a negative electrode for a nonaqueous electrolyte secondary battery according to claim 7

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